1. Field of the Invention
The present invention relates to a stage apparatus, control system, exposure apparatus, and device manufacturing method and, more particularly, to a technique using a laser interferometer.
2. Description of the Related Art
Conventionally, a laser interferometer having a helium-neon (He—Ne) laser as a light source is used to measure the coordinates of a moving member such as a stage. The laser interferometer capable of accurate measurement is suitable for accurate control of a moving member. The optical path wavelength of a laser beam emitted from the laser interferometer can change depending on the refractive index of the atmosphere (gas). For this reason, it is necessary to compensate for the change in the optical path wavelength of the laser beam.
Japanese Patent Laid-Open No. 2000-331904 discloses wavelength compensators for executing such compensation, including a compensator that calculates a wavelength change amount indirectly by detecting the atmospheric pressure, temperature, or humidity by a sensor and a compensator that directly detects a wavelength change amount by separately preparing a dedicated interferometer.
However, it is generally difficult to install a wavelength compensator near the optical path of a laser interferometer (to be referred to as a “moving member measuring interferometer” hereinafter) to measure the coordinates of a moving member. For this reason, the wavelength compensator is located in a place different from the moving member measuring interferometer. When the wavelength compensator is located in a place different from the moving member measuring interferometer, a conditioner for the wavelength compensator is also often installed separately from that for the moving member measuring interferometer, and the conditioning environments may be different. This generates an error in the wavelength compensator and degrades the measurement accuracy of the moving member measuring interferometer.
A gas conditioned by a conditioner can change its temperature, atmospheric pressure, humidity, and the like periodically as the time elapses. Such a periodical change is very small and hard to eliminate using a compensator in a control system. If the temperature, atmospheric pressure, humidity, and the like of the gas change, the refractive index of the gas can change and vary the optical path wavelength of a laser beam of the moving member measuring interferometer. This degrades the measurement accuracy of the moving member measuring interferometer.